As long as you’re not selling the phone afterwards I’d say the only thing stopping you would be the skill and knowledge required to do such a thing and the necessary tools.
Keep in mind most of the parts you’re talking about are to some extent proprietary and specifically designed not to be cross compatible, so that may be a big hurdle
I keep seeing this come up in various forums lately, and I don’t get it… The whole point of memes is that they are heavily shares isn’t it? That’s part of the literal textbook definition of what a meme is lol